Exposure meter



Feb. 20, 1940. H. SAUER Er AL 2,191,414

EXPOSURE METER Filed Feb. 2, 1938 2 Sheets-Sheet 1 Feb. 20, 1940. SAUERET AL 2,191,414

EXPOSURE METER Filed Feb. 2, 1938 2 Sheets-Sheet 2 Patented Feb. 20,1940 UNITED STATES PATENT OFFICE assignors to -Zeiss lkon Dresden,Germany Application February 2, 1938, Serial No. 188,874 In GermanyJanuary 13, 193'! 12 Claim.

This invention relates to improvements in exposure meters, andparticularly to improvements in exposure meters permanently combinedwith photographic cameras.

; It is an object of the invention to increasethe sensitiveness of themeter by utilization of a reflecting galvanometer as a part of theexposure meter.

It is furthermore an object of the invention to l facilitate the readingor the indicating beam by lengthening the path of the indicating beambetween the movable mirror of the galvanometer- 3 mirror may bepositioned out of line with the inlet opening for the light, and wherebyan optical element for focusing the light may be inserted between theinlet opening and the mirror of the galvanometer. 1! It is furthermorean object of the invention to render beam deflecting means adjustable inorder to cause the beam to appear ona predetermined point of atranslucent screen on which it is to be observed, and to combine theadjustable deflecting means with means for controlling the exposure. Itmay, therefore, also be described as an object of the invention tocombine a beam regulating means with an exposure control means of l thecamera, .whereby upon the appearance of the beam at a predeterminedpoint of the translucent screen, indication is furnished that thecontrol means for the exposure has been adjusted to the desiredposition.

With these and numerous other objects in view, an embodiment of theinvention has been described by way of example in the followingspecincation and shown in the accompanying drawings to which referenceis made in the speciilca- 7 tion.

In the ,1 Fig. 1 is partly a top plan view and partly a horizontalsection through a camera combined with an exposure meterand mirrorgalvanome- (Ci. 8H8) Fig. 4 is a rear elevation of the camera with theobservation window for the indicator beam, and I Y Fig. 5 is asimplified diagrammatical representation of the exposure meter and theoptical 5 equipment.

In the embodiment illustrated by way oi! example, the exposure meter isshown as being combined with the housing I oi=a camera. The lat-- terhas a mounting 2 preierably detachable, for 10 a suitable lens I. andisalso provided with exposure control means, as for instance, a diaphragmring 4' through which the effective aperture oi the-lens 3 may bevariedas demanded by the light conditions and other conditions for thexp sure. The diaphragm itself is not shown in r The means for focal.adiustmentot the lens I may be constructed in any desired=way and donot form any part of the present invention. Similarly. also, theconstruction of the diaphragm may be selected as desired, and no claimis made to the specific construction of these parts.

The exposuremeter illustrated by way of example also is o! the knowncurrent generating type in which the light striking a photosensitivecell energizes said cell to produce an electric current, the intensityor which depends upon the strength ofilluminat'ion. The intensity ofthis current may be determined by a galvanometer within the circuit.Devices of this type are now generally known-and are frequently employedeither in fixed association witirtbe camera itself or detached from thecamera.

In the embodiment illustrated, the front wall ofthe camera has anopening in which the photosensitive cell 5- is located. The electriccurrent generated upon him ination of the cell is carried throughconductors, not shown; to the movable system or a galvanometer I, thestationary part or which is formed by the-magnet I. A variableresistance I, I ig. 2, may be interposed between the source of current Iand the measuring instrument 8. and as in similar devices of thischaracter, the-variation of the resistance is eflected by supporting thesame movably relatively to a stationary contact member I in thecircuit.v

While in photographic exposure meters the movable system 0 of thegalvanometer generally causes a pointer to move relatively to a scale,so in thepresent invention the sensitiveness or the instrument isgreatly enhanced by converting this galvanometer intoa'g'fmirrorgalvanometer, and by providing a longer-path for the beam of lightreflected by the mirror than it normally would be in an instrument ascompact and compendious as instruments of this character necessarilyhave to be.

For this purpose the indicating beam of light reflected from the mirrorof the galvanometer is reflected, preferably a plurality of times,between the mirror l0 and the translucent observation window, so thatthis path is considerably longer than the actual distance between themirror "I and the translucent screen.

The front wall of the housing I is provided with a small or narrow slitll shown near the bottom and through which the light enters to strike areflector l2 preferably in a fixed position in the interior of thehousing. The light reflected by the mirror I 2 is thrown upon anothermirror or reflector l3 to be reflected thereby upon the galvanometermirror M.

For the purpose of producing a very sharp picture of the beam of lightentering the slit H in the housing, means for condensing said beam maybe provided between the point of entry and the movable reflector I0 01'the galvanometer. By way of example a compound lens ll adapted toproduce a very sharp picture of the beam of light is shown interposedbetween the reflectors l2 and it in the embodiment illustrated. Owing tothis multiple deflection, the location of the mirror It also need not bein alinement with the slit ll, so as to make the instrument very compactand narrow, without sacrificing the sensitiveness due to the mirrorgalvanometer.

The beam 01 light reflected by the mirror II is not projected directlyupon the translucent screen, but its path also is lengthened to producea broad sweep over said screen. In the embodiment shown, the beamreflected from mirror I! is directed toward the reflector l3 although itis obvious that in place of this reflector which had been used for theincident beam of light, an-

other reflector might be positioned in the path of the reflected beam.The light is then reflected from mirror l3 to a reflector l5, from whichlast named reflecting means it is projected upon the translucent screenIt. This screen is preferably disposed in the rear wall of the camera,and as shown in Fig. 4, a plurality of markings H are provided thereonpermitting the observer to read the position of the indicator beam llwith respect to any 01' these indications.

One of the deflecting. means is coupled with one or the elements forcontrolling the exposure conditions.

In the embodiment illustrated, the reflector us is mounted on a shaft20, which is rotatable in the housing. The upper end of shaft enters thebearing stud is, which may be fixed in the housing. A bevel gear 2! onshaft 2|] is in operative relation to the bevel gear 22, with which atrain of spur gears 23, 24 and 25 is associated, the last named gearbeing fixedly connected with another gear 26 in mesh with the gear rim28 on the ring 29, and this last named ring is connected with thediaphragm ring 4 of the camera. The adjustment of the resistance 8 iseffected by turning a knob. 30 which is accessible from the outside ofthe housing and which has a bevelled base 3| adapted to be setselectively with respect to a flxed mark 32 also disposed on thehousing. The bevelled disc 3| preferably carries indications of theshutter speed, and by rotation of the knob 30, therefore, the shuttermay be set to the speed indicated for which purpose a mechanism, notillustrated herein, but well known by itself, may be used. 2

In the use of the device, the operator advisably selects throughrotation of the knob It the exposure time which may depend upon thenature of the object, whether movable or stationary, and which also maybe selected under consideration of the light conditions as estimated bythe operator. Rotation of knob 30 not only adjusts the shutter to thedesired speed, but also I upon the light condition, and on the otherhand upon the resistance -8. The current imparts movement to the mirrorIt, so that the beaml8 travels over the screen It at the rear iace'ofthe camera. This rear face is directed towards the operator, and hencethe location of the beam is continuously under .observation of the user.The translucent screen I6 has markings II which may indicate the stop tobe used at the selected shutter speed. It is also feasible, however, toturn now the ring 34 which is connected with the diaphragm ring 4 andhas a diaphragm aperture scale 35 thereon, in order to actuate the trainof gears 28 to II inclusive, whereby a rotary movement of the adjustablereflector II is setup, thereby influencing the position of the beam onthe face of the transparent screen.

. 'l'his adjustment, preferably, is continued until the beam it reachesa predetermined position, as forv instance, a zero or central. positionupon the screen.

diaphragm for the speed which previously had been selected.

The invention, however, is not intended to be limited to the embodimentdescribed and shown.

It is possible for instance to effect positive setting ot the secondadjustable exposure control.

It could also be accomplished by having a sec- 0nd beam, or otherindicator means, in lagging or leading cooperation with the indicatorbeam.

7 We claim:

1. A photographic exposure meter comprising a housing, a photoelectriccell fixedly secured to a wall of said housing, a galvanometer providedwith a movable mirror indicator. within said housing, the wall of thehousing to which said photoelectric cell is secured being provided witha slit, a translucent screen in another wall or said housing, tworeflecting members within the housing for reflecting the beam of lightentering said casing through said slit onto said movable mirrorindicator, one of said reflecting members being positionedto reflect thebeam of light a second time, after said beam of light has been reflectedby said mirror indicator, 9. third refleeting member within said housingfor receiving the beam of light reflected from said mirror indicatoronto said last named reflecting memher and to reflect this beam of lightonto said translucent screen, and a manually operable means foradjusting said third reflecting member to direct the beam of light to apredetermined position on said translucent screen.

when this condition has been attained, the operator has selected theproper 2. A photographic exposure. meter comprising a housing, aphotoelectric cell flxedly secured to a;wall of said housing, agalvanometer provided a; slit, a translucent screen in another wall ofsaid housing, two reflecting members within the housing for reflectingthe beam of light entering said casing through said slit onto saidmovable mirror indicator, a beam concentrating objective between saidtwo reflecting members, one of said reflecting members being positionedto reflect the beam of light a second time, after said beam of light hasbeen reflected by said mirror indicator, a third reflecting memberwithin said housing for receiving the beam of light reflected from saidmirror indicator onto said last named reflecting member and to reflectthis beam of light onto said translucent screen, and manually operablemeans for adjusting said third reflecting member to direct the beam oflight to a predetermined position on said translucent screen.

3. A photographic exposure meter comprising a housing having a frontwall, a rear wall and a top wall, a photoelectric cell on said frontwall,

- a variable resistance and a mirror galvanometer within said housingand arranged in circuit with said photoelectric cell, said housinghaving a slit in its front wall and a translucent screen in its rearwall, means within said housing for reflecting the light beam enteringthrough said slit onto the mirror of said galvanometer, means forreflecting the beam of light reflected by said mirror onto saidtranslucent screen, manually operable means for adjusting said lastnamed reflecting means, and a second manually operable means on said topwall for adjusting said variable resistance, said two manually operablemeans being provided for directing the beam of light to a predeterminedposition on said translucent in its front wall and a translucent screenin its rear wall, means within said housing for reflecting the lightbeam entering through said slit onto the mirror of said galvanometer,means for reflecting the beam of light reflected by said mirror ontosaid translucent screen, manually operable means for adjusting said lastnamed reflecting means, and a second manually operable means on said topwall for adjusting 'said variable resistance, said two manually operablemeans being provided for directing the beam of light to a, predeterminedposition on said translucent screen, one of said manually operable meansbeing associated with a scale indicating shutter speed values and theother manually operable means being associated with a scale indicatingdiaphragm aperture values to indicate a shutter speed-diaphragm aperturecombination giving a correctly exposed negative when the beam of lighthas been adjusted to said predetermined osition on said translucentscale.

5. A photographic exposure meter comprising a housing, a photoelectriccell flxedly secured to a wall of said housing, a variable resistanceand a galvanometer provided with a movable mirror indicator within saidhousing and arranged in circuit with said photoelectric cell, the wallof the housing to which the photoelectric cell is secured being providedwith a slit, a translucent screen in anotherwall of said housing, means.within said housing for reflecting the light beam entering through saidslit onto said mirror indicator, means for reflecting the beam of lightreflected by said mirror indieatoronto said translucent screen,manually'f'operable means ior'adjustingsaid last named reflecting meansand a second manually operable means for adjusting said variableresistance, said two manually operable means being provided fordirecting the beam of light to a predetermined position on saidtranslucent screen.

6. A photographic exposure meter comprising a housing, a photoelectriccell flxedly secured to A a wall of said housing, a variable resistanceand a galvanometer provided with a movable mirror indicator within saidhousing and arranged in circuit with said photoelectric cell, the wallof the housing to which the photoelectric cell is secured being providedwith a slit, a translucent screen in another wall of said housing, meanswithin said housing for reflecting the light beam entering through saidslit onto said mirror indicator, means for reflecting the beam of lightreflected by said miror indicator onto said translucent screen, manuallyoperable means for adjusting said last named reflecting means, and asecond manually operable means for adjusting said variable resistance,said two manually operable means being provided for directing the beamof light to a predetermined position on said translucent screen, one ofsaid manually operable means being associated with a scale indicatingshutter speed values and the other manually operable means beingassociated with a scale indicating diaphragm aperture values to indicatea shutter speed-diaphragm aperture combination giving a correctlyexposed negative when the beam of light has been adjusted to saidpredetermined position on said translucent scale. 7. A photographicexposure meter comprising a housing, a photoelectric cell flxedlysecured to a wall of said housing, a variable resistance and agalvanometer provided with a movable mirror indicator within saidhousing and arranged in circuit with said photoelectric cell, the wallof the housing to which the photoelectric cell is secured being providedwith a slit, a translucent screen in another wall of said housing, meanswithin said housing for reflecting the light beam entering through saidslit onto said mirror indicator, said means including two reflectingfaces and a beam concentrating objective between the same, means forreflecting the beam of light reflected by said mirror indicator ontosaid translucent screen, manually operable means for adjusting said lastnamed means, and a second manually operable means for adjusting saidvariable resistance, said two manually operable means being provided fordirecting the beam of light to a predetermined position on saidtranslucent screen.

8. A photographic expolui'e meter comprising ahousinghavingafrontwall,arearwallanda top wall, a photoelectric cell on said iront 'wall,

a variable resistance and amirror galvanometer tioned to reflect thebeam of light a second time after said beam has been reflected by saidmirror, a third reflecting member within said housing for receiving thebeam of light reflected from said mirror onto said last named reflectingmember and to reflect this beam of light onto said translucent screen,manually operable means mounted on said front wall for adjusting saidthird reflecting member, and a second manually operable means mounted onsaid top wall for adjusting said variable resistance, said two manuallyoperable means being provided for directing the beam of light to a.predetermined position on said translucent screen.

- 9. A photographic exposure meter comprising a housing having a frontwall, a rear wall and a top wall, a photoelectric cell on said frontwall, a variable resistance and a mirror galvanometer within saidhousing and arranged in circuit with said photoelectric cell, saidhousing having a slit in its front wall and a translucent screen in itsrear wall, two reflecting members within the housing forreflecting thebeam of light entering through said slit onto the mirror of saidgalvanometer, one of said reflectors being positioned to reflect thebeam of light a second time after said beam has been reflected by saidmirror, a third reflecting member within said housing for receiving thebeam 01' light reflected from said mirror onto said last namedreflecting member and to reflect this beam of light onto saidtranslucent screen, manually operable means mounted on said front wallfor adjusting said third reflecting member, and a second manuallyoperable means mounted on said top wall for adjusting said variableresistance, said two manually operable means being provided fordirecting the beam of light to a predetermined position on saidtranslucent screen, one of said manually operable means being associatedwith a scale indicating shutter speed values and the other manuallyoperable means being associated with a scale indicating diaphragmaperture values to indicate a shutter speed-diaphragm aperturecombination giving a correctly exposed negative when the beam of lighthas been adjusted to said predetermined position on said translucentscale.

10. A photographic exposure meter comprising a housing, a photoelectriccell fixedly secured to a wall of said housing, a galvanometer providedwith a movable mirror indicator within said housing, the wallet thehousing to which said photoelectric cell is secured being provided witha slit, a translucent screen in another wail of said housing tworeflecting members within the housing for reflecting'the beam of lightentering said casing through said slit onto said movable mirrorindicator, a beam concentrating objective between said two reflectingmembers, a third reflecting member within said housing for receiving thebeam of light reflected from said mirror indicator and to reflect thisbeam of light onto said translucent screen, and manually operable meanssaid housing, two reflecting members within the housing for reflectingthe beam of light entering said casing through said slit onto saidmovable mirror indicator, one of said reflecting members beingpositioned to reflect the beam of light a second time, after said beamof light has been reflected by said mirror indicator, and a thirdreflecting member within said housing for receiving the beam of lightreflected from said mirror indicator onto said last named reflectingmember and to reflect this beam of light onto said translucent screen,said translucent screen having marking thereon indicating diaphragmaperture values.

. 12. A'photographic exposure meter comprising a housing having a frontwall, a rear wall and a top wall, a photoelectric cell on said frontwall, a variable resistance and a mirror galvanometer within saidhousing and arranged in circuit with said photoelectric cell saidhousing having a slit in its front wall and a translucent screen with ascale in its rear wall, two reflecting members within said housing forreflecting the light beam entering through said slit onto the mirror ofsaid galvanometer, one of said reflecting members- HANS sauna. PAULooaucn.

